This invention relates to a digitizing method. More particularly, the invention relates to a digitizing method in which movement is effected along at least one axis under numerical control and along other axes under tracer control to obtain numerical data for specifying the three-dimensional shape of an object.
A digitizing method is available in which numerical data for specifying the three-dimensional shape of a model are obtained by moving a tracer head in the X-Y plane under numerical control, moving the tracer head along the shape of the model in the direction of the Z axis under tracer control, and sampling the present values along each axis at predetermined time intervals.
In this conventional digitizing method, a commanded position is taken as the present position with regard to the axis (numerical control axis) that is under numerical control, but the present position with regard to the axis (tracer control axis) under tracer control is obtained through a follow-up technique.
A present position monitoring method based on follow-up is one which the present position along an axis is monitored by counting a number of pulses each of which is generated whenever a motor for drive along the axis rotates a predetermined amount. The present position along the tracer control axis is the actual machine position.
With the conventional digitizing method, therefore, the present position along the numerical control axis is represented by the commanded position, the present position along the tracer control axis is represented by the machine position, and there is an error corresponding to the servo-system delay between the positions along the numerical control axis and tracer control axis. The problem that results is that highly precise digitizing cannot be performed.